Thermal insulating fluid

ABSTRACT

A THERMAL INSULATING FLUID FOR USE IN THE TUBING-CASING ANNULUS OF A STEAM INJECTION WELL. THE FLUID CONTAINS AS A MAJOR INGREDIENT A HEAVY MINERAL OIL, PREFERABLY HAVING AN API GRAVITY LESS THAN 30*. THE FLUID CONTAINS INGREDIENTS WHICH WILL FORM A WATER-INSOLUBLE SOAP WHEN THE FLUID IS HEATED. THE VISCOSITY AND INSULATION PROPERTIES OF THE FLUID ARE INCREASED BY THE INCORPORATION OF 2 TO 6 PERCENT WATER, A BENTONITE-ORGANIC BASE COMPOUND, AND FINELY DIVIDED ASBESTOS FIBERS.

United States Patent 3,642,624 THERMAL INSULATING FLUID John W. Howland, Puerto La Cruz, Venezuela, and Juan C. Rosso, deceased, late of Puerto La Cruz, Venezuela, by Elsa Vich de Rosso, Buenos Aires, Argentina; said Howland assignor to Gulf Oil Corporation, Pittsburgh, Pa. No Drawing. Filed Dec. 12, 1968, Ser. No. 786,543 Int. Cl. E21b 21/04; C04b 43/04 U.S. Cl. 2528.55 8 Claims ABSTRACT OF THE DISCLOSURE A thermal insulating fluid for use in the tubing-casing annulus of a steam injection well. The fluid contains as a major ingredient a heavy mineral oil, preferably having an API gravity less than 30. The fluid contains ingredients which will form a water-insoluble soap when the fluid is heated. The'vi'scosity and insulation properties of the fluid are increased by the incorporation of 2 to 6 percent Water, a bentonite-organic base compound, and finely divided asbestos fibers.

This invention relates to the thermal stimulation of Wells and more particularly to an insulating liquid to be inserted in the annulus between steam injection tubing and casing of a steam injection well.

One method that has been widely adopted to increase the rate of production of high voscosity oils from underground reservoirs is to inject steam down a well and out wardly into the reservoir to heat the oil in the reservoir. After injecting steam for a period that may range from a few days to a monthor more, the steam injection is stopped and the pressure Within the well reduced to cause flow from the reservoir into the well. When the rate of flow of oil from the reservoir intothe well diminishes, the steam injection is repeated to heat the reservoir again and increase the mobility of oil thathas moved during the production period from remote portions of the reservoir toward the well.

' A serious problem that has been encountered in steam stimulation processesis damage to the well casing. Although the steam is-displaced down the well through tubing, enough heatis transferred through the annulus from the tubing to thecasing to heat the casing to high temperatures. The thermal expansion of the casing may break the bond between the casingandthe surrounding cement. If the casing is anchored-at spaced intervals in the well, for example, by cement at th ebottom of the well and attachmerit to larger casing 'at the top of the well, the heating of the casing may cause it to buckle or corkscrew. Reducing flow of heat from the tubing to the casing not only reduces the loss of heat to the surrounding formation, but also lowers the maximum temperature reached by the casing.

This invention resides in'a thermal insulating fluid for filling the annulus between the tubing and casing in a steam injection well. In the thermal insulating fluid composition of .this invention a small amount of water is dispersed in astable emulsion in a heavy mineral oil. The composition includes soapforming ingredients, specifi cally, lime and fatty acids which react adjacent the steam injection tubing to form a coating of soap on the tubing and to form a gel after the injection of steam begins. Bentoniteorganic base compoundsand asbestos particles are dispersed through the composition to provide a thick stable thermal fluid that has high gel strength and yet retains mobility to facilitate removal of the fluid after the steam injection.

Theessential characteristics of athermal fluid for re- Patented Feb. 15, 1972 "ice ducing the transfer of heat from the tubing of a steam injection well to the surrounding casing are a low thermal conductivity, a high viscosity or gel strength to reduce convection currents and thereby reduce transfer of heat by convection, and an opaqueness that will reduce radiation from the tubing to the casing. The thermal fluid should be stable both with respect to maintaining a mobility that will permit the fluid to be removed from the Well and with respect to retention of its gel strength to minimize settling of solid particles in the composition. It is preferred that the fluid be thixotropic to make possible a low viscosity during pumping of the thermal fluid into the annulus and a high gel strength to prevent settling of solids after the liquid is in place.

The mineral oil in the thermal fluid of this invention is a heavy oil of high boiling point that will not crack substantially when subjected to temperatures of approximately 650 to 700 F. for long periods. Heavy crude oil or crude oil residues are suitable mineral oils. A preferred mineral oil is a mixture of a heavy residual fuel oil (Bunker C) and diesel fuel oil. Refractory mineral oils such as visbroken residues of petroleum are especially suitable. The mineral oil constitutes about 60 to 80 percent by volume of the thermal insulating fluid. If a mixture of Bunker C fuel oil and diesel fuel oil is used, the

. Bunker C fuel oil may constitute from about 55 to 75 percent by volume of the composition and the diesel fuel oil from about 5 to 15 percent by volume of the composition.

It is important that the thermal insulating fluid maintain a high viscosity when heated to the high temperatures that are reached in the annulus between the tubing and easing of steam injection wells. The retention of the desired viscosity is aided by the dispersion through the composition of a small amount of the order of 2 to 6 percent water to form a stable gel with the soap. The presence of water further aids in the saponification of the fatty acids.

The soap-forming ingredients included in the composition react when heated by the injection of steam to deposit on the outer surface of the steam injection tubing an insoluble soap reducing the transfer of heat both by conduction and radiation, and which increases the viscosity of the fluid to reduce convection currents. Delay of the soap formation until after the fluid is in place facili tates filling the annulus with the insulating composition. The soap-forming ingredients include lime, which may be either hydrated lime or quicklime, and fatty acids having 12 to 18 carbon atoms per molecule. Preferred fatty acids are tall oil, a mixture of fatty acids and rosin acids, and tall oil pitch, which is obtained as a bottoms product in the distillation of tall oil, a composition containing other high molecular weight organic compounds in addition to fatty acids and rosin acids. The concentration of the soap-forming ingredients in the thermal insulating fluid is in the range of 10 to 20 percent by weight. It is desirable that the lime be present in slight excess of the stoichiometric amount required by neutralization of the fatty acids to insure a slightly alkaline condition to reduce corrosion of the tubing and casing.

The incorporation in the thermal insulating fluid of certain bentonite organic base compounds has been found to cooperate with the water to increase the thixotropy and gel strength of the thermal insulating'fluid with a consequent reduction in the rate of heat transfer through the fluid. The bentonite organic base compounds used in preparing the thermal insulating fluid of this invention are the reaction products of bentonite clay and such organic bases as aliphatic amines, their salts, and quaternary ammonium salts. The preferred bentonite compounds are quaternary ammonium compounds in which the N-substituents are aliphatic groups containing at least one'alkyl group with a total of at least 10 carbon atoms. When aliphatic amines are used in the preparation of the bentonite organic base compounds, the amines preferably contain at least one alkyl group of at least carbon atoms. A bentonite organic compound that has been found to be highly effective in the thermal insulating fluid of this invention is dimethyl dioctadecyl ammonium bentonite. The bentonite compound is incorporated in the thermal insulating fluid in amounts ranging from about 2 to 10 pounds per barrel (bbl.).

Finely divided asbestos is dispersed throughout the insulating fluid to thicken the composition and thereby reduce transfer of heat by convection. The concentration of the finely divided asbestos in the thermal insulating fluid should be in the range of 5 to percent by weight. Powdered asbestos is suitable. Finely divided fibrous particles or crysotile asbestos can be used in place of powdered asbestos. Because of the fibrous nature of the particles, their size is not accurately measured by the usual screening technique; however, a typical screen analysis of suitable asbestos fibers is:

0n U.S. Sieve Series: Percent 10 mesh 1.5

mesh 19 35 mesh 58.5

65 mesh 16 Pan 5 A thermal insulating fluid was prepared in accordance with this invention having the following composition:

Parts per barrel of insulating fluid 1 Dimetliyl dioctadecyl ammonium bentonite.

The composition set forth above was used tofill the annulus between the tubing and casing of a steam injection well in which steam was injected into a formation approximately 4,000 feet below the surface. Steam was injected at a temperature of approximately 600 F. for approximately 7 days. After completion of the steam injection, the well was produced at a rate of 300 barrels per day with a top hole temperature of 160 F. for approximately 5 weeks. A workover rig pulled the pumps and rods, and the thermal insulating fluid was pumped out of the well. A cement bond log run on the well showed excellent bonding of the entire interval and showed no change from the cement bond log run prior to steam injection. A comparison of before and after cement bond logs on 2 other'wells showed significant changes in the cement sheath. In both of the other wells good bonding before the steam injection had become nonexistent or very poor after the steam injection. Neither of the other wells had fluid in the tubing casing annulus during the steam injection, but the tubing in the injection string of one of the wells was aluminum coated tubing. Three samples of the thermal fluid were taken as' the fluid was pumped from the well. One sample was taken at the top of the well, one from the middle (2,000 feet plus or minus) and one from the bottom (4,000 feet plus or minus). The samples were tested for density, concentration of solids, and shear strength. The results tabulated below show that the thermal insulating fluid was stable and there was no measurable setting of the solids.

The effect of the bentonite organic base compound and water on the gel strength and thixotropic properties was tested by preparing compositions containing the Bunker C fuel oil, diesel fuel oil, tall oil and calcium oxide in the proportions set forth above for the thermal insulating fluid used in the well and varying the concentration of water and bentonite organic base compound. The initial gel strength and gel strength after 10 minutes were measured on a Fann viscometer. The difference in the two gel strengths is a measure of the thixotropic effect of the composition. The results of the tests are set forth in Table II:

TABLE II Sample Number Percent water 0 0 4 2 4 Lbs./bbl. bentonite compound.... 0 6 0 3 6 After aging 2 hours:

Initial gel 6 7 8 7 10 Gel after 10 min. 7 8 9 10 19 Thixotropie effect 1 1 1 3 9 After aging 16 hours:

Initial gel 8 14 7 13 17 Gel after 10 min 10 16 8 15 25 'Iluxotropie effect 2 2 1 2 8 It will be noted from Table II that the gel strength of Sample No. 5, which contains both the water and bentonite, is higher than the gel strength of any of the other samples. Moreover, the thixotropic effect of Sample No. 5 is at least three times the thixotropic effect of any of the other samples.

The insulating properties of the composition described above that was placed in the well were compared with a similar composition, designated as the control sample of mineral oil, soap-forming components and asbestos but not containing the bentonite compound and water, in a test cell consisting of a section of 2 /2 inch tubing mounted and sealed inside a section of 7 inch casing. A resistance Wire heater inside the tubing supplied heat to the tubing. Temperature measurements were made by thermocouples located on the outside of the 2 /2 inch tubing and on the outside of the 7 inch casing. The results of the tests are set forth in Table III.

TABLE III Input Tubing Casing Diff. Sample wattage temp., F. temp., F. temp., F.

Fluid I 216. 6 445 300 Control- 216. 6 412 151 261 Fluid I 253. 2 472 158 314 Control 254. 2 396 156 240 Fluid I 306.0 592 178 379 Control 306. 0 482 256 The thermal insulating fluid of this invention has excellent stability as well as excellent insulating properties. After an extended period in the tubing-casing annulus of a steam injection well, the fluid could be readily pumped from the annulus. Although the fluid was easily pumped,

80 percent by volume heavy mineral oil stable at tem peratures of approximately 650 to 700 F., 2 to 6 percent by volume water, 8 to 16 percent by weight fatty acid having at least 10 carbon atoms per molecule, 2 to 4 percent by weight lime, 1 to 3 percent by weight of a reaction product of bentonite and an organic base selected from the group consisting of aliphatic amines containing an alkyl group having at least 10 carbon atoms and a quaternary ammonium compound in which the N-substituents are aliphatic groups including an alkyl group of at least 10 carbon atoms, and to 15 percent by weight of finely divided asbestos.

2. A thermal insulating fluid as set forth in claim 1 in which the lime is quicklime.

3. A thermal insulating fluid as set forth in claim 1 in which the bentonite reaction product is a quaternary ammonium salt containing an aliphatic group having at least carbon atoms.

4. A thermal insulating fluid as set forth in claim 1 in which the fatty acid material is tall oil.

5. A thermal insulating fluid as set forth in claim 1 in which the fatty acid material is tall oil pitch.

6. A thermal insulating fluid as set forth in claim 1 in which the bentonite reaction product is dimethyl dioctadecyl ammonium bentonite.

7. A thermal insulating fluid as set forth in claim 1 in which the mineral oil is a visbroken petroleum residue.

8. A thermal insulating fluid for use in the tubingcasing annulus of a steam injection well comprising Bunker C fuel oil ga-ls./bbl 27.3 Diesel fuel oil gals./bbl 4.2 Water gals./bbl 1.68 Dimethyl dioctadecyl ammonium bentonite lbs./bbl 6.0 Tall oil lbs./bbl 42.0 Calcium oxide (quicklime) lbs./b-bl 10.0 Finely divided asbestos fibers lbs./bbl 40.0

References Cited UNITED STATES PATENTS 2,678,697 5/1954 Fischer 166295 1,860,622 5/1932 Rosenbaum 252316 X 1,965,935 7/1934 Blount et al. 252316 X 2,056,594 10/1936 Ambrose 2523 16 X 2,531,812 11/1950 Hauser 2528.5 M 2,776,112 l/1957 Ilfrey et al 2528.5 XM 2,808,338 10/1957 Bruno et al. 25262 X 2,888,357 5/1959 Pittman 25262 X 2,890,169 6/1959 Prokop 2528.5 P 2,995,514 8/1961 Jordan et al. 2528.5 M 3,176,354 4/1965 Blau et a1 25262 X 3,416,899 12/1968 Schifl 2528.55 XA HAROLD ANSHER, Primary Examiner U.S. Cl. X.R. 

